We present a detailed analysis of the state of surfaces of the 6.1 Angstrom family of semiconductors (InAs, GaSb and AlSb) under exposure to a nitrogen plasma. X-ray photoelectron spectroscopy (XPS) is used to determine the species created at the surface and their relative abundance. We find evidence that clean epitaxial surfaces exposed to the plasma form both V-N (SbN and AsN) and III-N (AlN, GaN and InN) compounds, but in different amounts and different proportions for each of the materials. (C) 2003 Published by Elsevier B.V.